Merge branch 'en/ort-perf-batch-15'

Merge branch 'en/ort-perf-batch-15'

Final batch for "merge -sort" optimization.

* en/ort-perf-batch-15:
  merge-ort: remove compile-time ability to turn off usage of memory pools
  merge-ort: reuse path strings in pool_alloc_filespec
  merge-ort: store filepairs and filespecs in our mem_pool
  diffcore-rename, merge-ort: add wrapper functions for filepair alloc/dealloc
  merge-ort: switch our strmaps over to using memory pools
  merge-ort: set up a memory pool
  merge-ort: add pool_alloc, pool_calloc, and pool_strndup wrappers
  diffcore-rename: use a mem_pool for exact rename detection's hashmap
  merge-ort: rename str{map,intmap,set}_func()